1. Field of the Invention
The present invention relates to a liquid crystal display device provided with not only a full-color display screen but also a monochrome display screen.
2. Description of the Related Art
Recently, in the area of mobile information terminals such as mobile phones and smart phones, light-weight, thin, and low-power liquid crystal display devices have been demanded. Liquid crystal display devices capable of displaying images in both reflective and transmissive modes (hereinafter, referred to as semi-transmissive liquid crystal display devices) have been used.
Further, in order to increase convenience, studies have been started to display a call status, an internet searching status and information searched, exchanged electronic mails, pictures taken by a camera, and the like on a full-color main screen, while auxiliary information including time, a battery status, news flash, and urgent information is always displayed on an auxiliary screen, a part of the main screen. However, since this auxiliary screen has to make the auxiliary information always viewable, there is a problem in that this type is more power-consuming than those without the auxiliary screens.
In order to solve this problem, there is known a method for displaying an image in a reflective mode in an auxiliary screen as disclosed in, for example, Japanese Patent Laid-Open Publication No. 2002-303863. However, with this method, front light is required in addition to outside light to secure sufficient brightness in the environments of everyday life. As the result, the power consumption increases.
In order to attain sufficient brightness without using front light, it is considered to remove a color filter from an auxiliary screen, as the color filter attenuates a third of brightness. In this case, the auxiliary screen becomes monochromatic and it thus mainly displays text information.
With this construction, monochromatic display by the auxiliary screen does not require front light but can still secure sufficient brightness in the everyday life environments, realizing adequate display quality for practical use.
However, a liquid crystal layer is generally an unaxial optical anisotropic substance where liquid crystal molecules in long axis direction and short axis direction have different refractive indexes, the wavelengths of light passing through the liquid crystal layer are dispersed. For this reason, the design of a liquid crystal display device with mere removal of a color filter has a problem in that white color display on an auxiliary is yellowed, resulting in notable degradation of display quality.